Elucidating the effects of photoperiod during gestation and lactation on mammary gene expression and function in cows and mice

• Author / Creator

  Bentley, Pamela AP

• Photoperiod, or day length, generates a highly accurate biological calendar that allows animals to anticipate and adapt to environmental change throughout the year. Photoperiod coordinates both daily and yearly rhythms associated with sleep/wake cycles, behavior, and reproduction, including mammary development and milk production. In dairy cows, long day (summer-like) photoperiod during lactation, or short day (winter-like) photoperiod during late gestation, enhances milk production. Potential mediators of these effects include changes in mammary cell-turnover and hormonal signaling factors. The effects of photoperiod on the mammary transcriptome and subsequently the molecular mechanisms underlying the milk yield response have not been elucidated. The aim of the work presented here is to identify genes and pathways responsive to photoperiod and associate their differential expression with functional effects of photoperiod in the mammary gland. To address this aim we employed microarray technology in two model systems, cows and mice, with the objectives of: 1. Evaluate the effects of photoperiod on the mammary transcriptome of cows. 2. Identify common effects of photoperiod on mammary function in cows and mice. 3. Evaluate the effects of photoperiod on the mammary transcriptome in mice. 4. Determine if physiological state (gestation or lactation) influences the effects of photoperiod on the mammary transcriptome. 5. Assess common biology between the cow and mouse models. In the bovine mammary gland, we identified 64 photoperiod responsive genes and have interpreted these genes and their associated functions in the context of the mammary gland. Differentially expressed genes were associated with mammary development and immune function consistent with the enhancement of milk production in the ensuing lactation. The transcriptomic signatures across time relative to parturition were not consistent with those in response to photoperiod, suggesting different underlying mechanisms. Furthermore, genes identified in the interaction of photoperiod and time indicate the physiological state of the mammary gland during late gestation influences its response to photoperiod. In the mouse, mammary cell proliferation and gene expression signatures provide substantial evidence that photoperiod can affect the ability of the mouse mammary gland to produce milk, although, we were unable to detect effects of photoperiod on litter weight. Overall, our findings provide several novel insights about the effects of photoperiod on the mammary transcriptome. Firstly, photoperiod manipulation is sufficient stimulation to affect the mouse mammary transcriptome. To that end, we have determined that long day and short day photoperiod affect very different sets of genes that are associated with distinct biological functions. In addition, photoperiod differentially affects gene expression in the mammary gland depending on the physiological state. Lastly, photoperiod can have enduring effects after the cessation of exposure on the mammary transcriptome. Ultimately, this work reveals that photoperiod manipulation induces changes in the mammary transcriptome during both lactation and gestation. The genes and pathways identified here have been grouped into six potential mechanisms that may underlie the effects of photoperiod on mammary development and function in cows and mice.

• Subjects / Keywords

  • Lactation
  • Mammary gland
  • Photoperiod
  • Gene-expression

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3PW5X

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.